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Are antibiotics turning livestock into superbug factories?

Almost 80% of all antibiotics in the United States aren’t taken by people. They’re given to cows, pigs, and chickens to make them grow more quickly or as a cheap alternative to keeping them healthy. These drugs could give rise to superbugs—bacteria that can’t be treated with modern medicine—and things are only getting worse. In 2013, more than 131,000 tons of antibiotics were used in food animals worldwide; by 2030, it will be more than 200,000 tons.

In a paper published today in Science, epidemiologist Thomas Van Boeckel of the Swiss Federal Institute of Technology in Zurich and colleagues outline the growing threat—and what can be done about it. Van Boeckel spoke to us about his team’s work. This interview has been edited for clarity and length.

Q: What are the threats posed by the overuse of antibiotics in food animals?

A: Most antibiotics are used either to prevent disease or to promote growth, and this means exposing healthy animals to antibiotics over long periods of time. If the bacteria that colonize these animals acquire [antibiotic] resistance genes, treatment becomes ineffective: That's a threat for the livestock sector because you can’t keep your animals healthy. But bacteria in the animals’ gut can also transfer the resistance genes to microbes harmful to humans. We don’t know the magnitude of this process, but given the large amount of antimicrobials used in animals we have good reason to be concerned. [In 2013, researchers showed that people living near pig farms or crop fields fertilized with pig manure are 30% more likely to become infected with methicillin-resistant Staphylococcus aureus bacteria.]

Q: What was the motivation behind your study?

A: Most countries have taken baby steps to limit the use of antibiotics in animals: For example, in the United States certain drugs can’t be used in food production, but loopholes in the legislation may still allow antibiotics to be used as growth promoters. If we are serious about antimicrobial resistance, we need more ambitious policies. Last year the United Nations General Assembly asked its member states to take measures to tackle the antimicrobial resistance problem. So we thought it was the best time to test if policies to reduce antibiotic use in animals could work at the global scale.

Q: How did you do that?

A: We collected data on antibiotic sales and prices for the countries that made them available. Then we tested three different strategies to reduce antibiotic use worldwide. The first one is cutting down meat consumption: In the United States, people eat on average 260 grams of meat per day. Reducing the meat consumption to 165 grams of meat per day—or four standard fast food hamburgers per person—would reduce the global consumption of antimicrobials by more than 20%. But recent history shows that people in low- and middle-income countries who can afford meat tend to eat more of it, so this can’t be the only solution the problem.

Q: What’s the other strategy you propose?

A: Last year, the O’Neill Review, a report on antimicrobial resistance, proposed a cap of 50 milligram of antimicrobials per year per kilogram of animal product. [At the moment there is no cap on antibiotic use.] We calculated that if we applied that cap to China and the member countries of the Organisation for Economic Co-operation and Development, we could reduce antibiotic use by 60%. The main challenge here is that if we want those legislations to work, they need to be enforced. And this means developing a surveillance system, which might be challenging on a global scale.

Q: What’s the third strategy?

A: Taxing the antibiotics used in agriculture when they come out of the factory or at the point of import. The idea—which is not new—is to make antibiotics more expensive so that farmers and veterinarians would only use them when necessary. Imposing a 50% tax on antibiotics for food animals could decrease global consumption by more than 30%, and at the same time generate revenues from $1.7 to 4.6 billion, which could be invested into research for new antibiotics or improvements to farm hygiene.

Q: Which one do you think is the most effective way to reduce global antibiotic consumption?

A: There's no silver bullet against it, and our solutions are not mutually exclusive. If the three measures were combined and fully implemented, we could reduce the antibiotic consumption up to 80%.

Q: What are the limitations of your study?

A: The main limitation is that there's little publicly available information on antibiotic sales and prices, so we had to rely on data from the 38 countries that made them available. It's crucial that more countries and the animal health industry report how much antibiotic is sold for animals: That would help us more accurately estimate the impact of each strategy.